1. Field of the Invention
The present invention relates to an L-glutamic acid producing bacterium and a method for producing L-glutamic acid. L-glutamic acid is widely used as a raw material in the making of seasonings and so forth.
2. Brief Description of the Related Art
L-glutamic acid is typically produced by fermentation utilizing the so-called coryneform bacteria, which belong to the genus Brevibacterium, Corynebacterium, or Microbacterium, or mutant strains thereof (Kunihiko Akashi et al., “Amino acid fermentation”, pp. 195-215, 1986, Japan Scientific Societies Press). Methods for producing L-glutamic acid by fermentation using other bacterial strains include using a microorganism belonging to the genus Bacillus, Streptomyces, Penicillium, or the like (U.S. Pat. No. 3,220,929), using a microorganism belonging to the genus Pseudomonas, Arthrobacter, Serratia, Candida or the like (U.S. Pat. No. 3,563,857), using a microorganism belonging to the genus Bacillus, Pseudomonas, Serratia, Aerobacter aerogenes (currently referred to as Enterobacter aerogenes) or the like (Japanese Patent Publication (KOKOKU) No. 32-9393), using a mutant strain of Escherichia coli (Japanese Patent Laid-open (KOKAI) No. 5-244970), and so forth. In addition, methods for producing L-glutamic acid using a microorganism belonging to the genus Klebsiella, Erwinia, Pantoea, or Enterobacter have also been disclosed (Japanese Patent Laid-open Nos. 2000-106869, 2000-189169, and 2000-189175). Moreover, it is known that the L-glutamic acid producing ability of Escherichia bacteria and coryneform bacteria can be improved by deleting the rpoS gene (WO01/05939).
The RpoS protein (also known as “sigma S factor”) encoded by the rpoS gene is not only known as a stationary phase-specific sigma factor, but also as a sigma factor which responds to various kinds of stress resulting in the control of various genetic expressions. More specifically, the sigma S factor plays a central role in acquisition of acid resistance, and it is reported that the survival rate of rpoS gene-deficient strains dramatically decreases under acidic conditions (Mol. Microbiol., 1995 Jul., 17(1):155-67). However, the majority of the research on acid resistance in microorganisms typically focuses on survival rate under acidic conditions, and there are no reports about growth under acidic conditions. In addition, growth of rpoS-deficient strains under acidic conditions has not been investigated to date.